Interval training: feel the burn

If you've ever queued indefinitely for the opportunity to buy over-priced choc ices and warm drinks in plastic glasses, you'll have a fair idea of how painful intervals can be. But in the world of running, the sort of intervals we deal with can be even more painful than shelling out a tenner for half a pint of lager and a Magnum.

A lot of training plans aimed at a specific race date will suggest that you do some intervals as part of the training. It's a session designed purely to help you cope with running at speed, and used well, it can do wonders for your times. Let's start by understanding what's involved.

When you decided to be a runner, the chances are you went through a period of mixing up running and walking, as you got used to the whole thing. For the same reason, you probably also like to run one day, and rest up for a day or two before running again. Sounds familiar? Then you'll be pleased to know that interval training is based on exactly the same principles, albeit with a greater propensity for puking. In simple terms, you run fast for a bit, then you take a bit of time to recover, and then you do the same thing again, repeatedly. For example, you might do six half-mile efforts, with two-minute recoveries in between.

The thing about intervals is that despite the rest periods, they are hard work. You might sail through the first effort with the wind in your hair and a smile on your face, but by the time you've done three or four, the breaks feel as if they're getting shorter, and your swearing gets louder – or at least it would do, if you had any breath to spare. But the buzz of elation that you feel for the rest of the day, knowing that you've done intervals, is better than any other session.

If you'll pardon the pun, it's important not to rush into interval training, especially if you're a novice runner. Bones, tendons, muscles and brains need time to adapt to the stresses of regular training. If you're running less than about twenty miles a week, then a gradual and consistent increase in your mileage should be enough to improve your times. But when you reach the point where you're running a decent mileage, but you've stopped improving, it's time to consider incorporating an interval session into your weekly routine.

So, how do intervals actually help? Hard-working muscles produce lactic acid. If you're running at a comfortable pace, your body has plenty of time to flush it away. But as you start to work harder and harder, there comes a point when your body can't do that quickly enough. The lactic acid starts to build up, leaving you with burning muscles and a desire to stop.

This point is called your lactate threshold, and interval training is all about encouraging your body to do all it can to offset this point, and to cope mentally when it does come – so you can run faster for longer. Your body responds to interval training by growing extra capillaries to transport more oxygen to your muscles, strengthening your heart to pump it round, and developing the capability to buffer more lactic acid.

The periods of effort need to be tough enough to push you just above your lactic threshold. Typically, your 5k pace is a good starting point, but if you use a heart rate monitor, you can aim for 85% of your working heart rate. You should aim to be able to run your final interval at the same pace you run your first one. Setting off like a scalded cat is counter-productive – it means you take longer to recover, and can compromise not just the rest of the session, but also your next training day. Adequate recovery between efforts is just as important – your body is still working hard to bring things back under control. Once again, it can take a bit of adjustment to get the length right.

In terms of the number and length of efforts, there are too many variations to list or recommend, and the choice of session can depend on your goal race distance, your fitness level, and your own preferences. Common sessions include 10 x 400m (with 60-second recoveries) right up to three or four mile-long efforts (with three-minute recoveries). Personally, I think it's useful to choose a different session each week. It keeps things fresh and mentally stimulating; and when you do come back round to the same session a month later, you should really nail it.

If you don't have a jazzy GPS watch, or a running track near you, you can still be in the gang. There are oodles of websites out there (including Fetcheveryone) where you can measure out a few streets or a footpath to get the approximate distance you need – or you can just base your intervals on time eg, four minutes fast, with two minutes recovery – and run where the mood takes you.

Take some time to learn what works for you – it's better to undercook the pace and overcook the recoveries. As you go on, your pace will improve, your recoveries will be quicker, and you'll be able to run for longer. Don't try to do it all at once – if you're going to shorten your recovery time or add an extra interval, don't try to run them faster too! A weekly interval session (with a week off every now and then) will do wonders for your race times, and give you the pick of the ice-creams, although it won't make the lager any cooler.

Some common interval sessions to get you started – please do suggest your own favourites below

• There's no limit to the number of different sessions you can do – from the straightforward to the downright twisted. The most popular are sessions such as 10 x 400m (with 60s rests) or 5 x 800m (2 min rests) or 3 x 1 mile (3 min rests).

• But you can also get inventive/cruel, and mix things up – for instance with a pyramid session: 400m, 800m, 1200m, 800m, 400m with rests between.

• Or if it takes you about eight minutes to run a mile, make the recoveries "10 minutes minus your mile time" – so if you slouch, you get less recovery time.

• If you've got a friend to run with, try running in opposite directions around a lake – one of you at pace, the other taking it easy. When you pass each other, you change roles. So long as you remember the core reasoning behind what you're doing, you can play about with the session to keep it fun. You'll still be swearing by the end though.